Reports show an atomic ratio for CIGS thin film solar cells by EDX analysis. How much is the accelerating voltage that is proper for applying? Is the atomic ratio different for different accelerating voltage? Or is it right to have different atomic ratio for different accelerating voltage?
The determination of the chemical composition of a thin film by EDX requires to follow some precautions:
- Choose the acceleration voltage according to the thickness of the film to be analyzed (typically for a film thickness of 350 nm take 10kV, but for 1µm take 20 kV, see the penetration depth of the incident electrons to adapt the acceleration voltage to the film thickness)
- Make a calibration of the analysis system (see the manual of your system) at the acceleration voltage that you will use
- Start with an analysis of a reference film (of same thickness) having a known composition
- Choose among the mathematical treatment proposed by the analysis system that which gives a correct analysis of the reference film
- Finally analyze your film of unknown composition in at least 3 places and make an average
With this procedure, you can have a precision of about 2-3% on the analysis of the film of unknown composition.
Dear Zahra,
I fully agree with the previous answer from Gilles Poullain.
Since the typical thickness of CIGS films is ~1-3 µm and often has a double Ga-gradient, you should use a high acceleration voltage, i.e. a large excitation volume, to get a most accurate composition of your film.
In addition, you may use different acceleration voltages in order to do a rough depth profiling of your composition. You may also check/confirm the composition of the CIGS layer with other techniques such as XRF.
Dear Torsten
Thanks for your complementary answer.
So, Do you mean that whenever a one parameter reports in the literature, it means using 20 KV acceleration voltage?
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